Question

这是完美的，直到订单进入，其中stationID不是= 2。我的逻辑是sql搜索两个条件满足并显示那些结果，而不是查看timeplaced的最大值，如果stationid不= 2则不显示它正在做什么。

SELECT OrderNo 
FROM   Orders 
WHERE  TimePlaced = (SELECT max(TimePlaced) FROM Orders) 
       AND StationID=2

Answer 1

将您的条件添加到内部选择中

SELECT OrderNo 
FROM   Orders 
WHERE  TimePlaced = 
       (
           SELECT max(TimePlaced) 
           FROM   Orders 
           WHERE  StationID=2
       ) 
       AND StationID=2

但是如果你不想两次添加条件，那么只需将内部选择与外部选择“链接”：

SELECT OrderNo 
FROM   Orders O
WHERE  TimePlaced = 
       (
           SELECT max(TimePlaced) 
           FROM   Orders 
           WHERE  StationID=O.StationID
       ) 
       AND StationID=2

您可以尝试的另一种方法是使用CTE和ROW_NUMBER：

;WITH OrdersCTE AS
(
    SELECT *,
           ROW_NUMBER() OVER(PARTITION BY StationID ORDER BY TimePlaced Desc) AS rn
    FROM   Orders
)
SELECT * 
FROM   OrdersCTE 
WHERE  rn = 1
       AND StationID = 2

SQL max函数与另一个条件不起作用

1 个答案: